neovo H-W22S black screen

[alessio211734]

Hello everyone,
I have a problem with a neovo H-W22S monitor.
When I turn on the screen, the image is visible for an instant
and then disappears. If I go to light up the screen with a flashlight with much difficulty
I can see the image. The monitor led remains on.
I unmounted the monitor and took some photos of the power board.
I add a video link to better understand the problem https://www.youtube.com/watch?v=ycyO...ature=youtu.be
Capacitors do not seem swollen. What could I verify?

[budm]

Re: neovo H-W22S black screen

Did you check the red rectangular fuse in the cold side next to the filter caps?

[momaka]

Re: neovo H-W22S black screen

Did you check the red rectangular fuse in the cold side next to the filter caps?

I imagine that should be okay, since the O/P says the monitor does show an image for an instant when turned On.

That said, can we see a higher resolution/quality picture of the power supply underside (solder side), please? Depending on the inverter transformer arrangement, I think one of the two driving MOSFETs either for the lower or the upper backlights may be bad, given the heat in the area. Of course, the problem could also be in one of the inverter transformers or one of the backlights.

[alessio211734]

Re: neovo H-W22S black screen

Thanks for reply, I checked the two fuses and they are ok. I upload a new photo in high resolution about solder side. Next steps?

[momaka]

Re: neovo H-W22S black screen

Thanks! It makes the troubleshooting process much easier.

Looks like the whole board must have ran hot, give the darkening. And from these pictures, it appears some components have ring cracks on their solder joints - most notably pins 1 and 2 on inverter transformer T801 (upper right corner of the picture you posted above).

Output rectifier D906 (TO-220 device mounted on a heatsink on the opposite side of the board) also appears to have a cold solder joint on the common cathode pin.

So I suggest starting by resoldering those joints, as well as all other joints on both inverter transformer, just to make sure that is not the issue.

If the monitor still has the same problem, then I suspect there may be something wrong with the inverter. With the CCFL lamps disconnected and monitor disconnected from the wall, measure the resistance on the output of the inverter transformers - that is, pins 7 and 8 on inverter transformers T801 and T802. The two resistance reading should match to within 5%, I think. But post what values you get here anyways.

Another possibility for the problem is transistors (likely dual MOSFET packs) Q802 and Q803. If you have the tools and experience to remove these (not too hard, but mention this anyways, as there may be other easier/simpler tests we can perform before we jump into removing components), get their datasheet and check if they are okay out of circuit. I can't quite make out their part number, but again, these are very likely dual MOSFETs.

That being said, can you also tell us the part number on IC801?

Last but not least, do you happen to have another dead monitor by any chance or perhaps a dead CFL bulb. We can use either of those to check the inverter/backlights of your monitor by either using the CFL bulb in place one of the monitor's CCFLs or use the other monitor's inverter to try and power the backlights in this monitor to see if there are any dead CCFLs (and in addition to that, we can also use the inverter of this monitor to see if it can power the CCFLs in the other monitor, thus allowing us to check the inverter function completely).

[budm]

Re: neovo H-W22S black screen

OK, thanks for better picture of the bottom side of the board so now I can see that the red fuse F903 is not for the inverter section but the SMD FUSE F801 ('D' printed on top) is the fuse for inverter section, so check that fuse.
https://www.badcaps.net/forum/attach...7&d=1533325890

[alessio211734]

Re: neovo H-W22S black screen

Hello, i tried to do some test.
1. checked SMD FUSE F801 and it's ok.
2. resoldering T801 and D906 but monitor still has the same problem.
3. Misured resistance between 7 and 8 on inverter transformers T801 and T802
and had these results:
T801 0.474 kohm
T802 0.477 kohm

I tried to take a picture about IC801 but it's not so easy. I think maybe a TL494
After this I take a picture about Q802(9945N) and Q803(9945N) can you confirm that are in the red circle?
I could even try to unsolder these components I have a hot air smd station even if I've never used it. But I do not know how to check if they are working.
Do you think this is their datasheet ? If you suggest me a how test them I will do it.

For the CCFT lamp test I have a old lcd laptop monitor working. Could use it?

[budm]

Re: neovo H-W22S black screen

At this point I would use two CCFL (or CFL) for testing the inverter circuit.

[alessio211734]

Re: neovo H-W22S black screen

I get one ccfl from my old laptop and followed this guide to test inverter.

a) TURN POWER OFF and unplug the monitor and wait 1 minute
b) disconnect CCFL #1 and plug in spare CCFL into spot #1
c) plug in monitor and turn monitor on - note if "2 seconds to black" occurs
d) TURN POWER OFF and unplug the monitor and wait 1 minute
e) reconnect CCFL #1 and disconnect CCFL #2 and plug in spare CCFL into spot #2
f) plug in monitor and turn monitor on - note if "2 seconds to black" occurs
g) TURN POWER OFF and unplug the monitor and wait 1 minute
h) reconnect CCFL #2 and disconnect CCFL #3 and plug in spare CCFL into spot #3
i) plug in monitor and turn monitor on - note if "2 seconds to black" occurs
j) TURN POWER OFF and unplug the monitor and wait 1 minute
k) reconnect CCFL #3 and disconnect CCFL #4 and plug in spare CCFL into spot #4
l) plug in monitor and turn monitor on - note if "2 seconds to black" occurs

I had the same result for each inverter output connector, spare CCFL stay up for less of 1 second and then go off. Can you suggest me other test?

[budm]

Re: neovo H-W22S black screen

You do not have two test lamps?
Condition of the laptop lamp?
BTW, did you check the resistance between Source and Drain of the Q802, 803 Dual MOSFETs?

[alessio211734]

Re: neovo H-W22S black screen

No I have only one test lamp. Laptop lamp I think it's good, because in laptop it was working.
I follow this guide for test Q802 e Q803:

Simply test

a) black on pin S1- red on pin G1 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

Repeat for the "2" pins. That is S2-G2, S2-D2, G2-D2.

Every pair of pin tested have a high resistence between 1 kohm and 1 mega ohm.
I check the voltage on the C802 and C803 and is 16 volt before push power on button, and at the instant the lamp lights up tension drop to 14v and when the lamp go off tension became 16v again. Please suggest me other test.

[budm]

Re: neovo H-W22S black screen

The problem of using just one test lamp is that you could have two bad lamps.
When I work on inverter that use 4 lamps I will use two test lamps for testing.
Bad worn out lamp will still light up but it will trigger over current shutdown.
I have lots of lamps: https://www.badcaps.net/forum/showth...274#post807274

[alessio211734]

Re: neovo H-W22S black screen

hello,
thanks for reply, I read in another thread where you said that it's possibile to use a resistor
to replace a lamp (you said about 125k resistor 8w).
I would ask you if it's possibile use 10 resistor 1.2 megaohm in parallel
to replace a lamp? I tried to looking for a cfl lamp or a t5 but can't find it
for less than 16 euro.

[budm]

Re: neovo H-W22S black screen

You will have to put a bunch of resistors in series for the resistors to handle up to 1500V, you need to find out what the breakdown Voltage rating of the resistor is.

[alessio211734]

Re: neovo H-W22S black screen

Hello,
I found this lamp on eBay I wanted to know if it could work to test the inverter. Should I connect 2 lamps of these to an inverter and the other two lamps of the monitor to the other inverter?

[alessio211734]

Re: neovo H-W22S black screen

Today I extracted the lamps from the LCD,
and I saw that surely 2 are broken I do not know if also 3.
I took 2 photos at the ends of each lamp group.
lamp1a,lamp1b is a group of 2 lamps and lamp2a,lamp2b is the other group of 2 lamps.
Now I would ask if the broken group lamp2a-lamp2b goes off the inverter circuit.
I would like understand if a broken lamp can stop a single inverter or both inverter circuit.

[budm]

Re: neovo H-W22S black screen

It will take only one bad lamp to activate the protection circuit and shutdown the whole inverter circui. it is also a reason you need at least 2 test lamps.-

[alessio211734]

Re: neovo H-W22S black screen

I think I found the solution. I connect one inverter to another monitor lamps and one inverter to lamp1a-lamp1b group and this time lamp1a-lamp1b stay on!
I would like replace my lamps. Do you know where can buy it?

[momaka]

Re: neovo H-W22S black screen

I've bought from CCFLWarehouse before, and all went well. But I live in US, so shipping was a no brainer. Looks like they do international shipping as well, but that might be prohibitively expensive for you in Italy (or elsewhere in Europe, probably).

Another option is to convert your monitor to LED backlights. I've briefly read a few threads on this forum where people did that. And the LED backlights are usually cheaper than a single or dual CCFL replacement. They're readily available on eBay and other websites like that too. I can't say how easy or hard it is to do or how long they last as I haven't done this mod myself. But in any case, it's an option that I think might be useful to keep in mind.

[alessio211734]

Re: neovo H-W22S black screen

Hello,
I replaced the lamp and assembly the monitor but now I saw some pattern on lcd some vertical black lines. I attached some photos.
And backlight suffer again some problem because sometime monitor stay up for 15 minutes and more and sometime come to black in 1 second.